A solar energy primer

How does it work? 

The sun emits light rays – even on cloudy days. When these rays hit a solar panel, the photons from the sunlight are absorbed by the semiconducting material in the panel, which is usually silicon. The energy from the photons (light particles) bump electrons loose, which then move between the negative and positive layers of the solar cell. This produces an electric current – a Direct Current or DC electric current, which is captured by the wiring in the panels. Because the home uses Alternating Current (AC), the energy must be converted from DC to AC – and that is the job of the inverter. The cables from the panels lead to the inverter which converts the energy and then sends it to power the home or export to the grid.

But not all PV technology is equal; choosing the right technology is pivotal to how much energy will be produced over the lifetime of your system and how much it will reduce your daily energy costs.  The technology you choose also has significant implications on the safety of the system, which in turn protects your employees, property and ensures business continuity.

String Inverter Technology

With this traditional solar technology, the panels are wired together in a string (hence the name). The inverter converts the power from DC to AC and is connected to the grid and to the home. It’s a simple and serviceable system – but has several limitations. In this system, each panel must be identical and placed at the same angle and tilt. These design constraints limit the way in which the installation area can be exploited, while limiting the ability to take advantage of the sun’s changing direction at different hours of the day. Newer, higher powered solar panels cannot be added in the future, unless the entire string is replaced. And significantly, production will be limited to the amount of energy the lowest performing panel on each string produces, meaning that panels that could potentially produce more, underperform to work in unison with all the other panels.

There are also safety limitations to this topology: panel voltage cannot be turned off, leaving panels at high voltage during the day, even when the inverter or AC power is turned off.

OEM providers and installers cannot remotely or easily check on panel performance, and troubleshooting on these types of installations can be more complex, as there is no way of remotely identifying the exact location of a problem. If an issue does arise or production drops significantly, the installer needs to check each panel to identify the location of the problem, which is time-consuming for the installer and wastes precious production time for the site owner. This can have implications for the consistency of production, as well as system safety. If a safety problem arises, it can take time to discover the source of the problem.

SolarEdge Innovations - DC Optimization and Power Optimizers

SolarEdge introduced some smart innovations that tackles the drawbacks of both of those systems.   In our system the inverter is installed safely on the ground. However, it shifts certain functions of the traditional inverter to a device called Power Optimizers while keeping the DC to AC function and grid interaction in the inverter. As a result, our inverter offers a smaller solution with advanced efficiency and reliability. As the system grows, the inverter can benefit from economies of scale, making our technology viable for large commercial and small-scale utility applications.

Power Optimizers are connected to each panel, making real-time adjustments of current and voltage to the optimal working point of each individual PV panel. This enables each PV panel to continuously produce its maximum power potential independent of other panels in the same string. By performing these adjustments at a very high rate, panel mismatch, partial shading losses and other power losses associated with traditional inverters are limited.

This also allows for system design flexibility; more panels can be installed to increase solar production and make optimal use of available space, as they do not need to remain in line with each other. Newer, more powerful panels could be added to a system after it was installed if the system were to expand in future. With real-time remote visibility on every panel of the system, easy and quick troubleshooting solves problems before they can develop, and sometimes, even remotely.

The Power Optimizers also enable including safety features at a panel level, which significantly increases safety on the site. In fact, many insurance companies and oversight bodies recognize MLPE (Module Level Power Electronics, which includes Power Optimizers) as significant for ensuring safety on a site. SolarEdge sees safety as an integral part of design and has innovated multilayered safety features to protect the site at every stage - during installation, production and maintenance.  Our extensive safety features include SafeDC™, designed to secure the work environment for first responders and maintenance teams by reducing high voltage on each panel to touch safe levels during grid or inverter shutdown, as well as features that can detect temperature increase even before a hazard can develop.  Read more about our safety features and approach here.  While the page is specifically focused on commercial sites, the approach and features are mostly applicable for residential sites as well.